Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$242.31	11.808%	$270.922	$270.92	$270.90	$270.90
Purchase #2	$193.86	13.349%	$219.7384	$219.74	$219.75	$219.70
Purchase #3	$71.56	6.713%	$76.3638	$76.36	$76.35	$76.40
Purchase #4	$115.97	3.665%	$120.2203	$120.22	$120.20	$120.20
Purchase #5	$74.46	5.439%	$78.5099	$78.51	$78.50	$78.50
Purchase #6	$36.87	9.688%	$40.442	$40.44	$40.45	$40.40
Purchase #7	$17.30	6.223%	$18.3766	$18.38	$18.40	$18.40
7 purchase totals =	$752.33		$824.5730	$824.57	$824.55	$824.50